Our overall objective is to use the aged canine to identify effective intervention strategies to reduce age-related cognitive decline and to prevent or reverse cellular and molecular events linked to cognitive dysfunction. We have shown that a diet enriched with antioxidants (AOX), both alone and in combination with behavioral enrichment (ENR), can improve and maintain cognitive function in aged dogs. The current proposal aims to refine our understanding ofthe mechanisms responsible for improved cognition and reduced brain pathology, building on our progress from the current grant period. We have demonstrated that the treatments reduce oxidative damage, improve mitochondrial function, reduce hippocampal neuron loss, and support neurogenesis. Interestingly, our recent data suggest that p-amyloid accumulation was not a primary target of the interventions, consistent with recent studies in humans. Rather, the interventions may be targeting cell health directly by curtailing pro-degenerative pathways driven by protease cascades. In Aim 1, we will follow up on our recent discovery that the interventions attenuate mechanisms of neuronal degeneration, in particular activation of caspase cascades. In Aim 2, we build on the success ofthe AOX and ENR inten/entions by teasing apart and optimizing the original ENR program. We test the hypothesis that long-term exercise intervention is the predominant ENR factor driving improved cognition and reduced age-related brain dysfunction. As in vivo indices of exercise-induced changes in brain function, we will use MRI to assess changes in cerebral blood volume and grey/white matter volume, and evaluate plasma and CSF biomarkers associated with aging and cognitive decline. In Aim 3, we will characterize the cellular and molecular changes induced in the brain by exercise to delineate mechanisms underlying cognitive improvements. A strength of the proposed design will be validation of physiological and cognitive changes assessed in vivo with post mortem histological findings so that the protocol may be applied to humans to monitor the acquired benefit of exercise for each individual. These results will be compared to our previous findings, and will allow the parcelling out of key factors contributing to successful aging.